As shown in FIG. 1, a motorcycle disk brake lock 1 of the present invention comprises a U-shaped main body 2 and a lock body 3. The main body 2 has a retaining slot 4 dimensioned to receive therein a motorcycle disk brake and provided in the inner wall of the left side thereof with a recess 5. The lock body 3 has a lock bolt 6 capable of moving back and forth over the retaining slot 4. In operation, the motorcycle disk brake is placed in the retaining slot 4 before moving the lock bolt 6 to pass the heat radiating hole of the disk brake to remain transversely over the retaining slot 4 in such a manner that the end of the lock bolt 6 is inserted into the recess 5 so as to secure the lock 1 to the brake disk. As the lock 1 is rotated along with the brake disk, the lock 1 is obstructed by the two shock absorbers mounted respectively on both ends of the wheel axle, so as to prevent the wheel from turning.
Such a prior art disk brake lock 1 as described above is defective in design in that the lock bolt 6 can be caused easily by an external force to become disengaged with the recess 5 by means of a tool, which is inserted into the retaining slot 4 to force one leg of the U-shaped main body 2 to move aside, as shown in FIG. 2.